This is a "proof of concept" study evaluating the mechanism of action of lumbar spinal manipulation. A fundamental hypothesis of chiropractic is that adhesions develop in the zygapophysial joints (Z joints) following hypomobility of these structures. Such adhesions are thought to be alleviated by separation (gapping) of the Z joints. Side posture adjusting is thought by many to gap the Z joints, yet no measurable differences of the Z joints before and after spinal manipulation have ever been published. The purpose of this study is to determine if differences can be measured in the L3-S1 Z joint spaces before and during side posture positioning of the lumbar region and also before and after lumbar side posture spinal adjusting. More specifically, this study will evaluate gapping of the L3/L4, L4/L5, and L5/S1 Z joints by taking measurements directly from MRI scans of the Z joints before and during positioning for a side posture adjustment and before and after side posture adjusting. To begin this study, healthy volunteers (32 female and 32 male) will be solicited. The volunteers will then be randomized into one of four groups: 1) neutral position followed by side posture positioning (trunk rotated to the subject's right), 2) neutral position followed by side posture spinal adjusting followed by neutral positioning, 3) neutral position followed by side posture spinal adjusting followed by side posture positioning, and 4) neutral position followed by neutral position (control group). MRI scans will be taken with the subjects in the original neutral position and in the final position (either second neutral position or side posture positioning). The experiments for each subject will be conducted over approximately a forty-five minute period. Three independent observers will be trained to make measurements of the Z joints directly from the MRI scans. The measurements will evaluate the anterior-to-posterior dimensions (gap) between the superior and inferior articular facets. The observers will not have access to the results of one another, and the MRI scans will be coded so that the observers will have no subject information and no indication as to whether any scan is pre- or post-treatment. The data will be analyzed to determine if differences exist between the before and during side posture positioning scans, the pre- and post manipulation scans, and the control group. The results of this 'proof of concept" study will be used to increase understanding of the mechanism of action of the lumbar side posture adjustment. If the results of this trial demonstrate gapping of the Z joints following manipulation, the next logical step would be the design and implementation of larger clinical trials using these same methods to evaluate the effects of side posture adjusting on the Z joints of subjects with acute and then chronic low back pain.